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Re: [OM] Homepage

Subject: Re: [OM] Homepage
From: Sean Mooney <smooney@xxxxxxxxxxxx>
Date: Tue, 16 Mar 1999 10:58:50 -0800
Cc: jowilcox@xxxxxxxxxxxxxxxxxxx
>>Right now I scan at 300 DPI, resize to 150 DPI, then "convert to web
>>image" at 90 DPI.  I am still new at this.  Others may have a better
>>technique.
>>How do you scan  for the best results on the web?
>>
>>John
>>
>John,
>
>PMFJI, but all things being equal, you are probably better off avoiding any
>resizing that you can.  So if you want to print at 300 dpi, try to scan to
>that resolution.  If you have to resize, obviously it's best to resize
>downwards, so scan initially to your highest needed resolution.
<
>
>Remember that an ordinary photographic print usually has only about 100 dpi
>worth of detail in it (so I'm told), or at the most about 200 dpi.  But
>apparently scanning to the desired resolution for whatever output you want
>and avoiding resizing is the ticket to the highest quality output.
>
>It looks to me as though you're doing it right, although I don't understand
>why you're resizing to 150 dpi as an intermediary step.
>
>Joel

        I'm not sure I agree.  Scanning at high res and resizing for the web
can be a good idea for a number of reasons.  First, for archival reasons a high
res digital image from a slide or print can act as a master were you can
resize in the future without loss of color or detail -- without having to
rescan.  Second, scanning at high res and resizing generally(IMO) gives a 
better 
image than a low res scan.  This comes about because often scanners require a
despeckle with perhaps a sharpening or blurring to the master, which upon
resizing gives a much better image.  Finally, editing is much easier on
a high res image than a low res one (such as manually removing spots, 
highlighting, adjusting balance, saturation, etc).

        I'm a little surprised there hasn't been a discussion about
gamma here.  Gamma could (arguably) be the most important consideration
when scanning and publishing images on the web.  The gamma values on
a pc is about 1.0 less than a mac which is about .5 less than an (default)
sgi.  Therefore images can appear to be a more than a stop lighter or darker
depending on what machine you are viewing them with.  Therefore, if you
have an image that is a little dark on an sgi, it will be too dark on a 
mac and nearly black on a pc.  Make sure you find middle ground that gives
good results on all systems.

Sean Mooney
Computer Graphics Laboratory 
University of California San Francisco

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